A variety of plasma antennas are known in the art. One type of plasma antenna, from Markland Technologies Inc. of Fredericksburg, Va., utilizes ionized gas enclosed in a tube or other enclosure as an antenna conducting element. In an arrangement of this type, electrodes are typically located at opposite ends of the hermetically sealed enclosure. Electrical discharge from the electrodes ionizes and excites the gas from a non-conductive gaseous state into an electrically conductive plasma state. The enclosure is formed in a particular fixed shape to provide the desired antenna configuration, such as a parabolic reflector configuration. A drawback of this type of arrangement is that the enclosure shape is fixed and thus cannot be reconfigured into other conductive arrangements. Flexible structures are not practical in such arrangements because they usually cannot be hermetically sealed at reasonable cost, when long lifetimes are desired.
A possible alternative plasma antenna approach is to confine plasma with magnetic fields, which allows the form and density of the plasma to be controlled in wide ranges by varying the magnetic field densities that are generated by electromagnets. However, electromagnets have the disadvantage of being bulky and represent conductive obstacles. They are therefore not suitable for use in antenna applications that depend on free propagation of electromagnetic waves.
It is also known to provide a reconfigurable antenna in which reflective elements are electronically “painted” on a reconfigurable conductive surface using plasma injection of carriers in high-resistivity semiconductors. Such techniques are disclosed in U.S. Pat. No. 6,567,046, issued May 20, 2003 to Taylor et al. and entitled “Reconfigurable Antenna,” and U.S. Pat. No. 6,597,327, issued Jul. 22, 2003, to Kanamaluru et al. and entitled “Reconfigurable Adaptive Wideband Antenna.” These semiconductor-based arrangements, however, are unduly complex, and require costly components.
Accordingly, a need exists for a reconfigurable plasma antenna which provides a high degree of flexibility in its possible configurations but without the cost and complexity commonly associated with semiconductor-based arrangements.